Condensation promoters

Table 9.6 shows the effect of both the addition time and the polarity of the solvent, as well as the nature of the aldehyde, in the catalytic asymmetric aldol condensation promoted by tributyltin fluoride and a chiral diamine coordinated to tin(n) triflate. 

A simple one-pot synthesis was described for tetrasubstituted thieno[2,3-/)]thiophenes 463 by condensation of 1,3-diketones with CS2, and alkylating agents carrying an EWG such as C02Et, COR, and CN in the presence of anhydrous KF or K2CO3 as condensation promoter in anhydrous DMF (Scheme 56) <199982030, 2001JHC1167>. 

Bigi, F., Carloni, S., Maggi, R., Mazzacani, A. and Sartori, G. Nitroaldol condensation promoted by organic bases tethered to amorphous silica and MCM-41-type materials. Stud. Surf. Sci. Catal., 2000, 130D, 3501-3506. 

Tanabe, Y. The selective Claisen and Dieckmann ester condensations promoted by dichlorobis(trifluoromethanesulfonato)titanium(IV). Bull. Chem. Soc. Jpn. 1989, 62,1917-1924. 

Ventron also offers Sodium borohydride-SWS, a stabilized water solution of average composition 40% sodium hydroxide and 12% sodium borohydride, sp. gr. 1.4. It is stable indefinitely and can be used as such for reduction of carbonyl compounds or it can be diluted with water, methanol, or ethanol. Most aldehydes are reduced so rapidly that condensations promoted by the alkali do not interfere. For reduction of an a,/3-unsaturated aldehyde, however, the strongly basic reagent is unsatisfactory and should be diluted to the desired concentration and neutralized with carbon dioxide. The neutralized reagent should be used immediately, since the borohydride is no longer stable and decomposes at 25° at the rate of 4.5% per hr. 

It should be noted that the only valid application of dropwise condensation is for steam condensers, since nonwetting substances are not available for most other working fluids. For example, no dropwise condensation promoters have been found for refrigerants (i.e., no dropwise condensation promoters seem to be Freon-phobic ) [46]. The enhancement of dropwise condensation, beyond inducing the process by selection of an effective, durable promoter, is fruitless, since the heat transfer coefficients are already so high. 

Promotion of Dropwise Condensation. Preliminary heat transfer experiments, using distilled water as feed, gave values of over-all heat transfer coefficient around 1000 B.t.u./sq. ft hr. ° F. and analysis indicated that the jacket condensate film provided the main resistance to heat transfer, due to filmwise condensation of the jacket steam. Following reports by Garrett (4) of successful tests using drop-wise condensation promoters, it was decided to use oleic acid for this purpose in the present experiments. The resulting improvement in jacketside coefficients enabled over-all heat transfer coefficients in excess of 5000 B.t.u./sq. ft hr ° F. to be achieved. 

The present results indicate that the spray evaporation technique provides a rapid and sensitive method for the investigation of scale formation on evaporator surfaces. Very high heat transfer rates are obtainable, especially when dropwise condensation promoters are used on the steam side, so that the effect of a thin film of scale becomes rapidly apparent. 

A correlation of the mass spectrometric results on water clusters around positive ions and the thermodynamics of water condensation promoted by ions is given in Ref. 43. 

Scheme 3.30 Aldol condensation promoted by basic sites in ammonia-doped r-GO.

Benaglia, M., Cinquini, M., Cozzi, F. and Celentano, G., Enantioselective catalysis in water Mukaiyama aldol condensation promoted by copper complexes of bisoxazolines supported on poly(ethylene glycol), Org. Biomol. Chem., 2004,2, 3401-3407. 

Davis and Forrester have studied the benzoin condensation promoted with a small ( 5 mol %) quantity of triethylamine and thiazolium salts (160). The reaction was accomplished when the thiazolium based organic ionic liquid (OIL) was stirred under nitrogen as a clearly heterogeneous mixture with a toluene solution of benzaldehyde. The reaction gave about 80% conversion to benzoin (163) (scheme-40) (Davis Forrester 1999). 

The 29Si NMR spectrum of an AAB sol after the second hydrolysis step (r = 2.5, dilution = 2 1) exhibits two broad peaks attributable to and Q3 species. There is no evidence of monomer or end groups/dimers consistent with a more extensive state of hydrolysis and condensation promoted by the additional acid-catalyzed hydrolysis step. The spectrum of an AAB sol (dilut 5 1) three hours after the third (base-catalyzed) hydrolysis step shows and (J species present in the proportions... 

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